OK, so you started multiple games and want the sims in the same game? I'll try to explain this simply.
You can only have one household as your active household in your game. You can however put sims you have created to live in the town, then you can switch between them if you want to control more than one family. This is done from "Edit Town", which you can find if you click the "..."-button at the lower left corner of the screen.
If you want to place sims from different saved games to one single game, you have to load each of them to your "library" first. Load the game and go to Edit Town. Then, click the houseicon of your sim family. There is a button to save the household to the bin. Do this to all the families you want to add to your other game.
Finally, load the savefile you want to use. Go to Edit Town and check households (there should be own tabs for households/sims, residential lots, and community lots). Click the sims you want to place on your town and you get the option to "place a copy" of them to the town.
I hope this was helpful! I tried to write simple instructions, but I play a translated game so there might be some differences. It's not difficult though to place sims to your town when you get to know the Edit Town menu. If there's any confusion, please ask again.
